1. Field of the Invention
This invention relates to the field of disposable thermometry, and, more particularly, the sub-fields of (1) the use of adhesives in disposable thermometry, and (2) the sub-field of materials used in conjunction with disposable thermometers containing temperature-indicating compositions of matter which change color with a change in phase.
2. Description of the Prior Art and Other Information
U.S. Pat. No. 4,232,552 to Hof and Ulin (not admitted as prior art hereto), incorporated herein by reference, disclosed a pioneer invention regarding novel and stable compositions of matter which change color sharply upon a transition from a liquid state to a solid state or from a solid state to a liquid state, which change of state is at substantially a predetermined temperature corresponding to a temperature to be measured. The constituents of the novel composition of matter comprise (1) a solvent (I) consisting of a single substance or a mixture of substances and adapted to change from a solid state at substantially a predetermined temperature to a liquid state, and (2) an indicator system (II) consisting of one or more substances different from (I), characterized in that:
(a) (II) is soluble in (I) when the latter is in the liquid phase, and
(b) the novel composition of matter, including the indicator system (II), changes color visible to the naked eye when (I) passes from the solid to the liquid phase, or from the liquid phase to the solid phase. When the '552 invention is employed in disposable thermometry, a preferred embodiment uses a mixture of ortho-chloronitrobenzene and ortho-bromonitrobenzene as a solvent and 0.035 weight percent pinacyanol iodide (of the entire composititon) as a dye indicator. The various solvent mixtures of ortho-chloronitrobenzene and ortho-bromonitrobenzene are varied in order to obtain different melting points for the thermometer. The thermometer generally has the melting points spaced from 96.0.degree. F. to 104.8.degree. F. at 0.2.degree. F. intervals (or 35.5.degree. to 40.4.degree. C. at 0.1.degree. C. intervals). The '552 compositions are substantially free of impurities, and are capable of being supercooled for at least several minutes. An unforseen problem in the use of '552 compositions in disposable thermometry is that many of the compositions are supercoolable not just for minutes, but, incredibly, for days, if not weeks, at conditions above 32.degree. F., i.e., household refrigerator conditions.
The use of heterogeneous nucleating agents to induce nucleation and crystallization of molten chemicals is well-known to those skilled in the classical opaque disposable thermometry art (see U.S. Pat. No. 3,980,581 to Godsey, Jr. et al. and U.S. Pat. No. 3,956,153 to Chadha), wherein a dye layer is employed beneath the solvent. Classical use of heterogeneous nucleating agents has been to employ the agents in the solvent of the temperature-sensitive mixtures, e.g., ortho-chloronitrobenzene and ortho-bromonitrobenzene used in such opaque thermometers manufactured prior to U.S. Pat. No. 4,232,552. For a review of the classicial thermometry art, see col. 1, line 40 to col. 6, line 19, of U.S. Pat. No. 4,232,552.
U.S. Pat. No. 4,189,942 to Giezen et al., incorporated herein by reference, discloses an opaque thermometer having a thermally conductive foil as a carrier layer, the carrier layer having one or more cavities formed by depression in the foil material. The depressions are filled with solid mixtures which melt at the predetermined temperatures and are composed of ortho-chloronitrobenzene, ortho-bromonitrobenzene and a dyestuff. The dyestuff is in a separate layer, and, when utilized, the Giezen et al. thermometer is non-reversible. A transparent layer cover seals the cavities and their contents. The transparent cover layer and carrier layer are bonded to each other by means of a pressure-sensitive adhesive which comprises polyisobutylene.
3. The Problem
Th surprising extreme lack of [reversibility] efficiency in the temperature-indicating compositions of matter of U.S. Pat. No. 4,232,552 poses a problem, inasmuch as it is desired to make the thermometers reversible in a short amount of time to those users in the hospital and the public who have access to only a common refrigerator, while, at the same time, maintaining the ability of the temperature-indicating compositions of matter to retain their supercooling properties for at least several minutes after the thermometer is used (otherwise, if the compositions were quickly reversed after use, i.e., withdrawal of the thermometer from the mouth, an accurate temperature reading could not be obtained).
4. An Invention
Surprisingly, in attempting to adapt the classical application of the heterogeneous nucleating agents in the temperature-indicating compositions of matter of U.S. Pat. No. 4,232,552, we have encountered some unforseen difficulties which severely restrict utility of prior art nucleating technology.
For example, the art as taught in Chadha, U.S. Pat. No. 3,956,153, is not operable in U.S. Pat. No. 4,232,552, because the Chadha nucleating agents taught therein are so efficient (i.e., raise the nucleation efficiency of the solid mixtures of the '552 compositions to such a degree) that stable supercooling at room temperature is not attainable, i.e., when the thermometer is drawn from the mouth, the compositions almost immediately revert back into solid form, making an accurate reading almost impossible. It is a requisite for use of the '552 temperature-indicating compositions of matter that they be supercoolable for at least several minutes, and this functional requirement is destroyed by use of the Chadha classical heterogeneous nucleating agents.
In Godsey, Jr. et al., U.S. Pat. No. 3,980,581, nucleating agents are taught which are substantially less efficient in inducing nucleation as to permit functioning of U.S. Pat. No. 4,232,552-type thermometers (e.g., TEMPA-DOT.RTM. READY-STRIP.RTM. thermometers sold by Organon Inc., West Orange, N.J.). An example of one such Gosey et al. nucleating agent is talc. These nucleating agents as taught in Godsey, Jr. et al. are heterogeneous in nature and insoluble in the liquid and solid phases of ortho-brominitrobenzene (OBNB):ortho-chloronitrobenzene (OCNB) based compositions. Unfortunately, the application of '581 insoluble nucleating agents to '552 disposable thermometers using state-of-the-art process machinery has presented additional problems deemed by us to be unsolvable. For example, if the powdered nucleating agent is sprinkled across the matrix of the thermometer in such a way as to insure that nucleating agents such as talc are contained in each pocket of the thermometer, the land areas between pockets on the carrier are invariably contaminated with the powdered nucleating agents. The contamination prevents effective bonding between the sealing member (i.e., adhesive of U.S. Pat. No. 4,189,942) and the thermometer base material. Furthermore, it has been found to be impractical to dispense these hard-to-handle powders in such a way that sufficient nucleating agent is contained in each pocket to induce nucleation at a specific temperature, while not adding so much that stable undercooling at room temperature is prevented. What was needed, then, was a nucleating agent and a means of applying same to the temperature-indicating compositions of matter of the '552 thermometer such that effective nucleation occurred at temperatures below room temperature (32.degree. F. to about 50.degree. F.), while the capacity of supercooling at room temperature was not substantially compromised such as to make the thermometer unworkable.
We found that a composition of matter, solid at room temperature, comprising:
(1) an effective amount of a suitable nucleating agent substantially uniformly dispersed in PA1 (2) a suitable pressure-sensitive adhesive for encapsulating a temperature-sensitive solid mixture having a given nucleation efficiency and which melts at a predetermined temperature, PA1 (1) an effective amount of a suitable nucleating agent substantially uniformly dispersed in PA1 (2) a suitable pressure-sensitive adhesive for encapsulating a temperature-sensitive solid mixture having a given nucleation efficiency and which melts at a predetermined temperature,
whereby the suitable nucleating agent is (a) inert to both the pressure-sensitive adhesive and the temperature-sensitive solid mixture, and (b) capable of raising the nucleation efficiency of said solid mixture, solves the problem.
More particularly, we have discovered that when talc, Mg.sub.3 (Si.sub.4 O.sub.10 (OH)).sub.2, is dispersed in a polyisobutylene (PIB) adhesive layer, and when this adhesive layer is used to seal the chemical pockets of a U.S. Pat. No. 4,232,552-style thermometer, that the regeneration of liquid pockets at temperatures from about 32.degree. F. to about 50.degree. F. is greatly enhanced when compared to similar thermometers in which the adhesive contains no talc. This is a surprising result to those skilled in the art. When a filler is incorporated in a polymer resin, it would not be expected to one skilled in the disposable thermometry art that one would find surfaces of the filler exposed at the surface of the polymer layer. Furthermore, as taught in Godsey, Jr. et al. above, intimate contact between the heterogeneous nucleating agent and the super-cooled melt are seen to be requirements for nucleation. Of course, the instant invention could be utilized not only for the novel temperature-indicating compositions of matter of U.S. Pat. No. 4,232,552, but also for the compositions employed in the classical, or opaque thermometers.
The invention has the added surprising benefit of reducing the complexity of manufacturing disposable thermometers when it is desired to use nucleating agents. This provides a significant reduction in the cost of manufacture over the addition of nucleating agents to the temperature-indicating compositions of matter sought by the prior art. Moreover, the mechanical problems of sprinkling or spraying the powdered classical nucleating agent on the molten area, freezing the temperature-sensitive materials and vacuum removing the dust have been avoided, together with the associated problems of attempting to make a uniform distribution of nucleating agents from pocket to pocket and from removing all the unwanted powder from the sealing surfaces.